Process of treating wet-spun acrylonitrile polymer fibers



July 30, 1963 R. B. HURLEY ETAL 3,099,517

PROCESS OF' TREATING WET-SPUN ACRYLONITRILE POLYMER FIBERS 2 Sheets-Sheet 2 Filed Deo. 16, 1960 Ex/ens/'on {perce/7%) xfems/'on (/oercenr) i? 6 yy 6 0 M2M ,1 Nuo a/Imc n wu 6m Wam/6K United States Patent 3,099,517 PROCESS 0F TREATING WET -SPUN ACRYLO- NITRILE POLYMER FIBERS Rupert B. Hurley, Williamsburg, Va., and Paul C. Colodny, Carmichael, Calif., assignors to The Dow Chemical Company, Midland, Mich., a corporation of Delaware Filed Dec. 16, 1960, Ser. No. 76,219 12 Claims. (Cl. 18-48) The present invention resides in the ield of synthetic tex-tile fibers and contributes to the art of their manufacture. More precisely, it relates to a useful and advantageous process for stretching or orienting Wet-spun acrylonitrile polymer iibers while they are in an aquagel state that are prepared by being coagulated from suitable spinning solutions or equivalent compositions (such as spinnable dispersions) in aqueous coagulating spin baths and subsequently washed with Water to remove residual spinning solution solvent from the freshly wet spun liber.

The invention has particular reference to the manufacture of acrylonitrile polymer fibers which are fabricated from ber-forming acrylonitrile polymers 'that contain in the polymer molecule at least about 80 weight percent of polymerized acrylonitrile, especially polyacrylonitrile, which are wet spun in and with systems that are adapted to utilize aqueous coagulating liquids for the spinning operation, such as systems wherein ethylene glycol, dimethyl formamide, dimethyl sulfoxide, butyrolactone and the like or the various aqueous saline polyacrylonitrile-dissolving solvents are employed as spinning solution solvents for the polymer and are also present in nonpolymer-dissolving quantities in the aqueous coagulating liquid used in the spin bath.

The urtile, known aqueous saline solvents for the various fiber-forming acrylonitrile polymers. and polyacrylonitrile include zinc chloride, the various thiocyanates such as calcium, lithium bromide, salt mixtures of the so-called lyotropic series, and `others recognized by the art, as has been disclosed, among other places, in United States Letters Patents Nos. 2,140,921; 2,425,192; 2,648,592; 2,- 648,593; 2,648,646; 2,648,648; 2,648,649; and 2,949,435. Advantageously, aqueous zinc chloride solutions are used for the purpose.

It is common knowledge to the man-made iiber art that most of the synthetic iibers must be stretched or oriented sometime during their manufacture. Depending on the crystallinity and/ or molecular configuration of the fiber, the amount of stretching and stretching conditions may differ widely. In some cases very little stretch is necessary, in others, the iibers may be stretched as much as i300-2000 percent. The stretching may be done cold =or hot, in air, Water or some other gaseous or liquid medium. ln all cases the intent is to align to some extent the crystallites or polymer molecules parallel to the iber axis. This alignment is necessary in order to take `advantage of the inherent tensile properties in the iibers.

Wet spinning of iibers generally involves spinning a solution of -a polymer dissolved in a solvent for the polymer into a non-polymer-dissolving liquid causing a polymerio filament to coagulate. The polymer solvent is thus washed or leached out lof the coagulated polymer and most often replaced with an inert liquid, frequently water. The iilament so formed is usually in a gel state, that is, it is highly swollen and may contain as much as 4 6 times -as much non-polymer-dissolving or inert liquid, eg., Water, as polymer. The gel iilament is usually washed, stretched, and, ultimately, dried to destroy the gel structure.

It is also well established in the art that the stretching lor orienting of acrylonitrile polymer wet-spun iibers is 3,099,517 Patented July 30, 1963 "ice usually don-e at temperatures inthe range of 70-1l0 C., and preferably at 90-100 C. in the presence of moisture. Ordinarily, high stretch ratios are only possible at the higher Itemperatures if undue filament breaking is to be avoided; and, stretch ratios Iof about 101:1 and higher are normally necessary to produce fibers with a satisfactory combination of physical properties. The total stretch given the fiber has been imparted in one step or in several sequential increments.

However, in the prior `art, no particular lattention has been paid to the sequence of stretching as associated with temperature, fthe principal interest lying solely in the desired ultimate stretch imparted to the iibers. Thus, any physical-property improvements in the fibers resulting from the stretch were dependent on the total stretch ratio applied to the bers. It remained, then, that avenues pursued to improving or altering the iber physical properties that could not be obtained through stretch ratios were those such as changing the polymer composition, eg. forming copolymers, and certain other treatments performed Ion the iibers after they had been substantially completely oriented, or yafter they had been oriented and dried.

It is the prime interest and concern of this invention to provide a process whereby in a continuous and consistently uniform manner wet-spun acrylonitrile polymer fibers can be made to have greatly improved physical properties without having to require the use of extreme alterations in normal wet-spinning techniques. In particular, it is an object of this invention to provide wet-spun acrylonitrile polymer ibers with increased physical properties by utilizing an especially advantageous process for stretching the substantially unstretched bers While they are in the gel state.

This invention takes advantage of the criticalities of the temperature-stretching sequence used during the stretching or orienting of wet-spun acrylonitrile polymer gel iibers. In accordnace with this invention, highly irnproved physical properties of the iibers can be obtained by; pri-or to imparting any substantial stretch to the gel i'ibers, i.e., less than about 1.5:1, they are contacted with an aqueous medium yat a temperature of from about 50 to about C. (for lat least about 2 seconds); setting the gel structure; and subsequently stretching said gel tibers while they are exposed to a heated medium maintained at from about 80 to about 110 C.

The treatment according to the invention, which in part might be best referred to as a gel-structurizing treatment, is thought to impart a particular morphological structure to the gel which in turn is thought to be responsible for the new improved and distinct properties of the resulting ber. The change in structure is observable when a typical stress-strain curve is run on the gel tre-ated as prescribed by the invention. lt is essential for satisfactory practice of the invention that this particular and beneiicially imparted gel structure be set in the gel filament before lany stretch is given to the lament at temperatures above about 80 C.

The setting of the structure can be accomplished by one of two methods: (1) The structure can be set by stretching the gel iilament while the filament is being subjected to the gel-structurizing treatment, that is, while being contacted with an aqueous medium at 50p-80 C. Any permanently elongating stretch is sufficient to set the gel. A stretch rati-o of 1:1.1 may be employed, but ratios of from about 2:1 to about 8:1 are more advantageous. (2) The iilament may be removed from the gelstruoturizing medium held at 50-80 C., more advantageously at 5 5 -75 C., and cooled to some temperature below that at which the gel-structurizing medium was maintained. The aqueous gel-structurizing medium is prefer- 3 ably essentially water but may contain other water-miscible materials inert to the gel filament, or other watermiscible or dispersible beneficial adjuvants desirous of being impregnated into the gel.

After either method, the fiber is then stretched in a subsequent heated medium `at 80 to ll0 C., preferably at 90 to 110 C., and advantageously at 95 to 100 C. A single subsequent stretch at 80ll0 C. or a sequential series of stretches at 80-ll0 C. may be employed. Either a liquid aqueous bath or a gaseous or vapor atmosphere such as saturated steam may be employed as the stretching medium.

In practicing the present invention, the gel structure imparted to the gel filaments or the change in the gel structure is irreversibly introduced as long as the structure is set by one of the methods hereinbefore set forth. For example, if a gel filament is treated at 70 C. and then cooled to 60 C. or lower and stretched, the gel structure will have the characteristics of the 70 C. ternperature treatment. The filament would have the same characteristics if stretched while being treated at 70 C. On the other hand, if a fiber were treated at 70 C. and then heated to 80 C. and stretched, the effects of the 70 C. treatment would be erased and the 80 C. treatment characteristics would prev-ail. In all cases, the highest temperature at which the gel structure is introduced, provided the structure is set at that or a lower temperature, will dominate the characteristics of the gel filament, and hence the physical properties of the resulting finally converted textile fiber. If a treating or gel-structurizing temperature is employed below about 50 C., no physicalproperty-improving characteristics are introduced into the gel. Similarly, but with different end results, above about 80 C., although a structure is introduced which has an effect `on the physical properties, the improvements 'are not evidenced that are brought about by treating in the range of 50-80o C. It should be m-ade clear that the benefits of this invention are not evidenced by a transient pass of the gel filaments through an aqueous medium at 50-80 C. to a higher temperature Without a setting step. In other Words, the treatment must be interrupted by either cooling to some lower temperature or stretching before exposing to la higher temperature.

As previously indicated, the characteristic change introduced into the gel structure by the 50-0 C. temperature treatment can be identified through observing a stress-strain curve obtained from a simultaneously recorded tensile test on the unstretched gel filament. (Frequently, a slight stretch of about 1.4:1 at 20-25 C. may be given the gel filaments after they are coagulated to give them enough strength for subsequent processing, but for all practical purposes, the laments are referred to as unstretched.)

lFIGURE l represents a typical stress-strain curve obtained from an unstretched wet-spun polyacrylonitrile gel filament that was treated in a water bath at 210-25 C.

FIGURE 2 represents a typical stress-strain curve obtained from an unstretched gel filament lfrom the same sample as the filament used for FIGURE l but which had been treated in a Water bath within the temperature range in accordance with the invention.

From a comparison of the typical curves of FIGURES l and 2, it is seen that an unusual peaking of the initial slope on the curve and then a falling back to the normal stress-strain curve itinerary is characteristic to gel filaments produced according to the invention. This peaking and return to the more usual post slope is absent in the curve of FIGURE l. Fibers made from gel filaments exhibiting this peaking type of stress-strain curve have highly improved physical properties as compared to fibers made from gel filaments with a stress-strain curvev shaped like that in FIGURE l.

The fibers produced according to the invention have highly improved tenacity, yield point, modulus, and transverse properties. One measure of improved transverse properties are the improved ywet fibrillation properties of the fiber. In addition, it is frequently desirable to impregnate the gel (or aquagel) filaments with :a dye additive, and, the instant process reduces the required amount of dye additive to obtain the same dyeability when contrasted to the stretching process common to the usual practice. Similarly, impregnation with other beneficial iadjuvants is improved.

General wet spinning techniques involve, in sequence; extruding the polymer dissolved in a suitable aqueous solvent or water-miscible solvent, coagulating to a polyrneric gel filament, washing the filament essentially completely free of residual solvent, imparting the desirable stretch or orientation to the filament, possibly followed by other miscellaneous treatments, and finally irreversibly drying the gel structure :to a characteristic textile fiber.

In the practice of this invention, the gel-structurizing treatment is preferably performed succeeding the washing step and necessarily preceding or partially simultaneously with the stretching or orienting step.

After their extrusion, coagulation, washing, gel-structurization and gel setting, the freshly wet spun filaments -may be subsequently handled and treated in any desired or necessary manner for purposes of converting them to a finished `fiber product. Thus, they may be stretched or otherwise :treated for purposes of heat treating or relaxing the fibers in any desired way or they may be subjected to additional treatments of any appropriate nature, including application lof finishes, lubricants and the like or imposition of :crimp prior to being dried and finally collected as completely manufactured products.

As has been indicated, when acrylonitrile polymer, particularly polyacrvlonitrile, fibers vare being manufactured, zinc chloride may most advantageously 'be utilized as the sole, or at least the principal, saline solute in the spinning solvent employed for the polymer. In such instances, the aqueous solution `of zinc chloride in the spinning solution may `advantageously be in a yconcentration of from 55 to 65, preferably about 60 percent by weight, based on the weight of the aqueous solution. When such aqueous Zinc chloride solvent spinning solutions are employed, it is desirable to maintain the concentration of zinc chloride in the portion of the liquid in the spinning zone -at a nonpolymer-dissolving coagulating concentration of iat least 25 percent by weight; advantageously from about 30 to 50 percent by Weight, and preferably between about 40 and 45 percent by Weight. In such laqueous Zinc chloride systems for acrylonitrile polymers, wherein the freshly wet spun polymer is generally obtained in 1an aquagel form, it is generally desirable for the spinning solution that is extruded to contain between about 4 and 20 percent by weight of dissolved polymer; more advantageously from about 6 to l5 percent by weight of dissolved polymer; and preferably, particularly when polyacrylonitrile fibers are being manufactured, from about 8.5 to 11.5 percent by Weight of fiber-forming polymeric solids in the spinning solution.

Aqueous zinc chloride spinning solutions of fiber-forming acrylontrile polymers lare beneficially extruded at a spinning temperature of from 0 to 50 C.; preferably from about l0 to 30 C., into an `aqueous Zinc chloride coagulating liquid that is maintained at .a coagulating temperature of from 0 to 30 C.; preferably from about l0 to 20 C. Thoroughly washed ac-rylonitrile polymer aquagel fibers, incidentally, are usually found to contain not more than 51/2 pa-rts by weight of water (including residual extrinsic or exterior Water associated therewith) for each part by weight `of dry polymer therein. More frequently, washed acrylonitrile polymer aquagel fibers are found to contain from Iabout 2 and usually from about 3 to 4 parts by weight of water for each part by Weight of polymer.

Homopolymeric acrylonitrile gel filaments or polymeric gel filaments formed Afrom copolymerizing acrylonitrile with one or more other ethylenically unsaturated monomers copolymerizable with acrylonitrile sucfhthat the copolymeric product contains -atleast about 80 percent by 'weight of acrylontrile polymerized in the polymer molecule may be lbeneficially and advantageously treated according to this invention. Examples of Iother monomeric materials which may be employed advantageously with acrylonitrile in the practice of the present invention include allyl alcohol, vinyl acetate, acrylamide, methacrylamide, methyl acrylate, 2-vinyl pyridine, dimethylamino- 'ethylacrylate methacrylonitrile, acrylic acid, itaconic acid, vinyl acetic acid, ethyl acrylate, fumaronitrile, Z-vinyl 5- ethyl pyridine, ethylene sulfonic 4acid and its alkali metal salts, allyl sulfonic acid and its alkali metal salts, vinyl lactams such as vinyl caprolactam and vinyl piperid-one, vinyl benzene sulfonic acid and its salts, vinylbenzene-trimethyl Iammonium chloride, vinylrnethyl ether, N-acryloyl Itaurina and its salts, Z-arnino-ethyl-methacrylate hydrochloride, 2 sul-foethylacrylate, X sulfopropylacrylate, maleic :anhydride and the like, including mixtures thereof.

In addition, the properties of certain other of the modified acrylonitrile polymer fibers may be beneficially enhanced by practice of the present invention, especially those that are comprised of the essential acrylonitrile polymer base, particularly polyacrylontrile, in which there has. been intimately and permanently lor substantially permanently incorporated minor proportions of form 1 -or 50 up to about 2O Ior so percent by weight, 4based on the weight of the polymeric composition Iof any of the beneficial additaments or constituents :adapted .to serve the desired purpose and provide the beneficial result. These referred-to polymeric compositions are frequently called acrylic alloys. Generally, such beneficial additaments are employed primarily as dyeeassisting adjuvants or components. Advantageously, they may be the polymerized products of such azotic monomers, or mixtures thereof, as the several N-vinyl lactams including such :broadly related products as the N-vinyl-Z-morpholinones; the N-vinyIl-Z-oxazolidinones; and certain of the N-vinyl-N-methyl-alkyl-sulfonamides.

Thus, the acrylic alloy may be comprised of the acrylonitrile polymer base that is prepared by graft or block copolymerizration of acrylonitrile or an acrylonitrile containing monomer mixture upon a minor proportion of an alreadyr formed polymer derived from any of the indicated varieties of azotic monomers or their mixtures. Or, as mentioned, it may consist of a graft copolymer product of any of the indicated varieties of azotic monomers on an already formed and preferably already fabricated acrylonitrile polymer base.

Advantageously, and frequently with consummate suitability, the acrylic alloy fiber may be comprised of the acrylonitrile polymer base in which there -is permanently incorporated by physical blending in minor proportion of any of the polymer products from the specified azotic monomers or mixtures thereof, primarily as dye-assisting adjuvants. The physical blending can be carried out prior to spinning of the fiber-forming solution, or as in the case of wet spinning, it can profitably be incorporated in ythe aquagel filament prior to irreversibly drying the aquagel.

As indicated, the adjuvant or beneficial constituent in the acrylic 'alloy fiber may be homopolymeric in nature or it may be a straight copolymer of any of the azotic monomers specified with other monoand polyfunctional monomers. Adjuvants of this variety are ordinarily physically blended with the essential acrylonitrile polymer base in order to secure the desired intimate incorporation of the beneficial constituent and the resulting alloying effect in the fiber. Likewise, there may be similarly utilized for physical blending purposes adjuvants or additaments that are graft copolymeric in nature and which consist of various monomers that are graft copolymerized on substrates consisting of polymers of any of the indicated azotic monomers, such as poly-N-vinyllactam substrates; poly-N-vinyl-Z-oxazolidinone substrates and poly-N-vinyl- N-methyl-alkylsulfonamide substrates. Similarly, just as suitably, graft copolymeric addit-aments may be provided and employed when they consist of any of the specified or closely related azotic monomers (such as N-vinyllactam monomers, N-vinyl-Z-oxazolidinone monomers and N-vinyl-N-methyl alkylsulfonamide monomers graft copolymerized on other functional polymer substrates.

It is usually beneficial for the polymer products of the azotic functional monomers to be present as the beneficial component in acrylic alloy fibers in an amount that is in the neighborhood or range of from about 5 to l5 percent by weight, based on the weight of the acrylic alloy composition. It is -frequently quite desirable to employ :a homopolymeric N-vinyllactam polymer, such as poly-N-vinyl-pyrrolidone (which may also be identified as poly-N-vinyl-Z-pyrrolidone or, with varied terminology, poly-N-vinyl-Z-pyrrolidinone), poly-N-vinyl caprolactam, or somewhat related thereto, a poly-N-vinyl-S-morp'holinone; or a homopolymeric N-vinyl-Z-oxazolidinone or poly-N-vinyl-S-methyl-Z-oxazolidinone; or a homopolymeric N-vinyl-methylalkylsulfonamide polymer such as homopolymeric N-vinyl-N-methyl-methylsulfon-amide; as

the polymeric adjuvant that is blended with the essentialV acrylonitrile polymer base in the acrylic alloy composition. When physically blended acrylic alloy products are prepared that utilize, as the beneficial additament or constituent, copolymeric or graft copolymeric products of the indicated azotic monomers, it is usually beneficial for the polymeric adjuvants that are employed to be those which are comprised of at least about 50 percent or even as much as or more percent by weight of the products of the indicated constituents derived from the azotic monomers.

Further features and advantages of the invention will be evlident from the following examples, which are presented with no intent of restricting or limiting the invention thereto. Unless otherwise indicated, all parts and percentages are by weight.

EXAMPLE l In order to exemplify the applicability of the :invention over a broad range of conditions, fibers were wet spun using widely differing conditions and then conditioned, or in contrast not conditioned, in accordance with the invention.

A spinning solution was prepared comprised of polyacrylonitrile with an average molecular weight between about 30 and 35 thousand dissolved in an aqueous 60` percent by weight solution of Zinc chloride. The total polymer solids in the spinning solution were about 10 percent by weight, based on the weight of the solution. Two sets of coagulating bath conditions were used for spinning the filaments:

An aqueous 47 percent by weight zinc chloride bath maintained at a temperature of 24 C. Plilaments spun into this bath were designated sample 'A.

An aqueous 43.4 percent by weight zinc chloride bath maintained at a temperature of 11 C. Filaments spun into this bath were designated sample B. The spinning solution was extruded into each of the coagulating baths, the coagulated gel filaments were washed essentially -free of residual salt, given a stretch of about 1.4521 at room temperature and collected. The gel filaments of sample B were more dense than those of sample A.

Individual gel filaments from each of samples A and B were selected at random and subjected to a tensile test at room temperature. The gel fibers were kept under ethylene glycol during the testing to prevent the gel from drying. Stress-strain curves were automatically recorded duning the tensile test which is the widely known and accepted procedure for determining the physical properties of fibers and filaments. lFive filaments were run from each sample. In FIGURE 3 is seen a typical stressstrain curve representing the curves obtained from the gel filaments of sample A. Likewise, FIGURE 4 shows a typical stress-strain curve obtained from the gel filaments of sample B.

`Other filaments were selected at random from sample B and subjected to a tensile test from which stressstrain curves were simultaneously obtained as described above, except, prior to being tested, they were each placed in a water bath each at a different temperature for a constant period of time, cooled back to room temperature, and then tested. Thus, fthe gel filaments were -given a igel-structurizinig treatment, some within the temperature range of the i-nvention, and some Without the range. FIGURES through 10 show representative curves typical of these obtained from the treated and tested filaments. Again, five filaments were tested for each sample. The results are summarized in Table I.

The typical curves in FIGURES 3 land 4 (samples A and B), which can -be considered as obtained from gel filaments treated at about 201 C. prior to testing, and the typical curve in FIGURE 5 (sample B1), obtained `from gel filaments treated at 50 C., ydo not exhibit any peaking of the initial slope as exhibited in the curves of FIGURES 6 through `8 (samples B2, B3 and B4 obtained yfrom gel filaments treated at 52-72 C. The typical curves of FIGURES 9 and 10 (samples B5 and B5), obtained fromigel lilaments treated at 82 C. and 100 C., exhibit a peaking of the initial slope but `do not exhibit a post slope such as those prominent in FIGURES 6 through 8.

The summation of physical property data in Table I is evidential of fthe fact that the most advantageous and beneficial combination of physical properties and of improvements in physical properties lie in the gel filaments that have been treated in accordance with the invention, and as a consequential corollary, those that are characterized in an abnormal peaking in their stress-strain curves and subsequent return to a normal post slope.

Similar excellent results were obtained when gel filaments from sample A were treated in water lbaths as was done with `gel filaments from sample B. Significant improvements were obtained in physical properties from the ttilaments treated in conformance with the invention, which filaments also exhibited the peaking effect in their stress-strain curves.

EXAMPLE 2 Gel filaments from sample B of Example 1 Were treated :for 1 minute and 10 minutes in a water bath at 65 C. and then cooled back to room temperature prior to being subjected to a tensile test.. The results are shown in Table II.

Although the results of Table II show slightly improved results for the longer treating time, for all practical purposes, the time is not particularly critical, since significant improvements are obtained when the treatment is imparted for only a few seconds, i.e., 5-10 seconds.

EXAMPE 3 Polyacrylonitrile ibers were spun from a spinning solution as described in Example 1. They were coagulated in an aqueous 44.5 percent by weight ZnClZ solution at 12 C., washed free of residual salt, given a 1.45 :1 stretch at room temperature, and then passed through two aqueous baths at 95-100 C. The filaments were stretched 3.4:1 in the first of the two baths and 2.4: 1 in the second bath. The total stretch was about 11.88: l. The gel fibers were then irreversibly dried at 140 C. for about 7 minutes to characteristically hydrophobic textile fibers. The final fibers, designated sample C, were then tested for physical properties including the tendency of the fibers to split ofi.E or peel back dibrils vfrom the fiber surface, commonly referred to as Wet fibrillation.

Two other fiber samples, samples D and Ef were prepared in the same Way as sample C, excep-t the conditions ofthe hot-wet stretching were changed to con- -form with the treatment of the invention. Sample D was passed through an aqueous bath at 69 C. and stretched 539:1 in the bath, and then through two aqueous baths at 95*100 C., being stretched 1,35:l in the rst bath and 1.19:1 in the second bath. The total stretch of sample D Was about 12.5:l.

Sample E was stretched 5.16:1 in a 67 C. aqueous bath and 1.32 in -l00 C. aqueous bath. The total stretch of sample E was about 10:1. The physical properties of samples D and E were determined as well as Wet fibrillation tendencies.

In further contras-t, fibers were produced according to the procedure of sample D except that a hot stretch of 5.3:1 was given in lan aqueous `67 C. bath and no 95- C. stretch followed. This sample was designated sample Ff The total stretch of sample F was about 8:*1.

The results of these four samples Vare given in Table III.

As mentioned previously, the resistance to Wet fibrillation of samples C, D, land E Iwere measured. 'Ilhis was 4determined through a standardized test which involves the use of a Waring Blendor for Wet fibrillating the tibers. More precisely, samples of fiber are cut to about 1/2 inch staple length iand weighed into 200 mg. lots -for the standardized test procedure.

After the samples Kare cut `and weighed the flow time for passage of one liter of water through :a pad of the material is determined. The pad of fibers is formed by pouring water Ithrough a l34" diameter by 3" cylinder with a screened bottom and a Weighted screen topi. Three passes of 300 ml. of Water through the device serves to make a uniform pad of the lber over the screen.

Next, [the cylinder containing the sample is placed in the bottom of the container which holds the water for the flow test `and the iiow time for the one liter of Water to pass through the sample is Idetermined with a stop watch.

When the initial fiow time has been determined, the sample is now ready for the Waring Blendor. The sample is Washed from the cylinder and sufficient water added to make up 100 tml. Standard testing calls for 10 minutes operation, with 100 ml. Water, Aand 75 watts power input to the blender. This treatment is then followed by another fiow time measurement and the percent change in iiow time recorded as the test result. Thus, the test is based on the principle that the more iibrillated the fibers the more dense will be the pad of fibers and hence the more resistance offered to the flow of water therethrough.

The resistance to wet fibrillation of sam-ples D and E were about two times and about four times, respectively, improved over sample C.

As `further exemplication of the benefits of the invention; a sample was prepared the same as sample C and poly-N-vinyl-Z-pyrrolidone (PVP) was inpregnated in the aquagel filaments in the lot stretch baths; approximately C7 percent PVP, 'based on the weight of the dry fiber, (OWF) was required to obtain a reflectance value of 21 when the 'bers were dyed with 2 percent (OWF) Calcodur Pink 2BL (Colour Index Direct Red 75). In contrast, when PVP was put into the hot stretch baths and the filaments treated according to the procedure of sample D, only 3.248 percent PVP (OWF) was required to obtain :a reflectance value of 21.

The dyeing with Calcodur Pink 2BL was performed at the 2 percent level according to conventional procedure in which the fiber sample was maintained for about one hour at the boil in the dye bath which contained the dyestuff in an amount equal to about 2 percent 0f the weight of the fiber. The dye bath also contained sodium sulfate in .an amount equal to about 15 percent of the weight of the fiber and had a |bath-to-ber Weight ratio of about 30: 1, respectively. After being dyed, the iiber was rinsed thoroughly with water and dried for about 20 minutes at 810 C. The dye-receptivity of the Calcodur Pink 2BL- dyed fiber was then evaluated spectrophotometrically by measuring the yamount of monochromatic light having a wave length of about 5120 rnillimicrons from a standard source that was reilected from the dyed sample. A nu- [merical value on `an arbitrarily designated scale from to 100 was thereby obtained. This value represented the relative comparison `of .the amount of light that was re- -flected from a `standard white tile reflector that had a reflectance value of 316 'by extrapolation from the 0-100 scale. Lower reflectance values are an indication of better dye-receptivity in the fiber. For example, a reflectance value `of about 2.0 or 25 to 50 or -so for acrylonitrile polymer fibers dyed With 2 percent Calcodur Pink 2BL is generally considered Iby those `skilled in the art to be representative of a degree of dye-receptivity that readily meets or exceeds the most rigorous practical requirements and is ondinarily assured of receiving general commercial acceptance and approval.

Commensurate excellent results to the foregoing are obtained when other acrylonitrile polymer gel bers, including .acrylonitrile polymers of the copolymeric variety or those of the Aacrylic alloy variety, .are treated in accordance with this invention which is encompassed in the hereto appended claims.

What is claimed is:

1. In .the method of wet spinning acrylonitrile polymer fibers which are fabricated from fiber-forming acrylonitrile polymers that contain in the polymer molecule at least about 80 Weight percent polymerized acrylonitrile,

any balance being another copolymerized ethylenically unsaturated monomer that is polymerizable with acrylo- 5 nitrile, the improvement which comprises; contacting substantially unstretched acrylonitrile polymer gel fibers with an aqueous medium 4at from about 50 C. to about 80 C.; lsetting the gel structure imparted to said acrylonitrile polymer gel fibers by means of cooling said gel fibers to a temperature below the temperature at which said aqueous contacting medium is maintained; and subsequently stretching said gel fibers While lthey are exposed to a heated medium from about 80 C. to about 110 C.

2. The method of claim 1, wherein said aqueous medium for contacting said acrylonitrile polymer gel bers is maintained at between about 55 C. and 75 C.

3. The method of claim 1, wherein said medium for contacting said acrylonitrile polymer gel fibers is essentially Water.

4. The method of claim 1, wherein said heated rnedium for said subsequent stretch is maintained at between about 95 C. and 100 C.

5. The method of claim 1, wherein said heated medium is an aqueous medium.

6. The method of claim l, wlherein said heated medium is saturated steam.

7. The method of claim 1, wherein said heated medium is water containing a minor proportion of a vinyl 'lactam polymer.

8. The method of claim 1, wherein said acrylonitrile polymer is polyacrylonitrile.

9. The method of claim 1, and including the step of irreversibly drying said -gel fibers.

10. The method of claim 1, wherein `said acrylonitrile 35 gel fibers are spun from Ian aqueous saline solvent for said acrylonitrile polymer.

11. The method of claim 10, wherein sai-d aqueous saline solvent is an aqueous solution of which the principal saline constituent is zinc chloride.

12. The method of claim 10, Aand including coagulating said acrylonitrile polymer gel fibers in a bath comprising the same saline constituents that are present in said aqueous saline solvent.

References Cited in the file of this patent UNITED STATES PATENTS 2,451,420 Watkins oct. 12, 194s S0 2,517,694 Merion Aug. 8, 1950 2,601,254 Bruson Jan. 24, 1952 2,611,929 Hoxie Sept. 20', 1952 2,715,763 Marley Aug. 23, 1955 2,790,700 Stanton Apr. 30, 1957 2,922,692 Messer Ian. 26, 1960 2,948,581 Cummings Aug. 9, 1960 

1. IN THE METHOD OF WET SPINNING ACRYLONITRILE POLYMER FIBERS WHICH ARE FABRICATED FROM FIBER-FORMING ACRYLONITRILE POLYMERS THAT CONTAIN IN THE POLYMER MOLECULE AT LEAST ABOUT 80 WEIGHT PERCENT POLYMERIZED ACRYLONITRILE, ANY BALANCE BEING ANOTHER COPOLYMERIZED ETHYLENICALLY UNSATURATED MONOMER THAT IS POLYMERIZED WITH AERYLONITRILE, THE IMPROVEMENT WHICH COMPRISES; CONTACTING SUBSTANTIALLY UNSTRETCHED ACRYLONITRILE POLYMER GEL FIBERS WITH AN AQUEOUS MEDIUM AT FROM ABOUT 50* C. TO ABOUT 80* C.; SETTING THE GEL STRUCTURE IMPARTED TO SAID ACRYLONITRILE POLYMER GEL FIBERS BY MEANS OF COOLING SAID GEL FIBERS TO A TEMPERATURE BELOW THE TEMPERATURE AT WHICH SAID AQUEOUS CONTACTING MEDIUM IS MAINTAINED; AND SUBSEQUENTLY STRETCHING SAID GEL FIBERS WHILE THEY ARE EXPOSED TO A HEATED MEDIUM FROM ABUT 80* C. TO ABOUT 110* C. 